Acronym of Latin Sancte Ioannes, the phrase ending the hymn Ut queant laxis from earlier words of which the other notes of solfège were derived.
si (plural sis)
Try searching for words with the letters SI, words with the phrase SI, words starting with the letters SI, or words ending in the letters SI.
Words… ending with q, starting with q, starting with qa, starting with qo, with two letters, starting with x, starting with j, ending with j,
Some random searches:
AUPKPT, NMTZNO, GOEN, ZPRA, PENTW, JUIOBG,